If your received emails from firstname.lastname@example.org, that look something like this, then don’t respond to it. This is one big scam. The people behind this e-mail offer your a good price for buying your domain and then trick you into an appraisal service that they own.
Example of a mail being sent:
I am interested in purchasing this domain name (not the website content, only the domain).
If you are open to selling please let me know ASAP and I will submit my best offer.
Thanks for your time,
Mike Howard (email@example.com)
They also use different email addresses.
Hope to have saved you some valuable time and money!